The present invention relates to a moisture-responsive valve, and particularly to such a valve for use in controlling the supply of water to plants in accordance with the moisture content of the soil in which the plants are grown.
Many moisture-responsive valves have been developed for use in water irrigation systems in order to control the supply of water to the plants in accordance with the moisture content of the soil. Such valves are widely used in irrigation systems wherein the water is supplied to the water irrigation devices periodically (e.g., water sprinklers), or continuously (e.g., water drippers), until the water content of the soil reaches a predetermined level, whereupon the supply of water is automatically terminated. Examples of known valves of this type are described in U.S. Pat. Nos. 4,648,555 and 4,696,319.
Such known moisture-responsive valves commonly include a moisture-swellable body which controls the flow. However, the known constructions generally do not permit the moisture-swellable body to expand to its limit. As a result, the moisture-swellable body may be subjected to a large force which can seriously degrade the body and substantially shorten its useful life.